Partial Order Trace Analyzer (POTA) for Distributed Programs

Abstract

Checking the correctness of software is a growing challenge. In this paper, we present a prototype implementation of Partial Order Trace Analyzer (POTA), a tool for checking execution traces of both message passing and shared memory programs using temporal logic. So far runtime verification tools have used the total order model of an execution trace, whereas POTA uses a partial order model. The partial order model enables us to capture possibly exponential number of interleavings and, in turn, this allows us to find bugs that are not found using a total order model. However, verification in partial order model suffers from the state explosion problem – the number of possible global states in a program increases exponentially with the number of processes.POTA employs an effective abstraction technique called computation slicing. A slice of a computation (execution trace) with respect to a predicate is the computation with the least number of global states that contains all global states of the original computation for which the predicate evaluates to true. The advantage of this technique is that, it mitigates the state explosion problem by reasoning only on the part of the global state space that is of interest. In POTA, we implement computing slicing algorithms for temporal logic predicates from a subset of CTL. The overall complexity of evaluating a predicate in this logic upon using computation slicing becomes polynomial in the number of processes compared to exponential without slicing.We illustrate the effectiveness of our techniques in POTA on several test cases such as the General Inter-ORB Protocol (GIOP)[18] and the primary secondary protocol[32]. POTA also contains a module that translates execution traces to Promela[16] (input language SPIN). This module enables us to compare our results on execution traces with SPIN. In some cases, we were able to verify traces with 250 processes compared to only 10 processes using SPIN.